The Drosophila nervous system is generated from a series of stem cells called neuroblasts (NBs). The goal of the research is to examine the relative contributions of lineage and positional cures to the specification of neuronal cell fates. This question is being studied in the gooseberry (gsb) expressing NBs and neurons in the Drosophila embryonic central nervous system (CNS). Drosophila offers certain unique advantages for studying nervous system development; genetic manipulation of the organism is relatively easy, the anatomy of the embryonic CNS is well described, and molecular techniques are extremely sophisticated. The questions to be addressed are; What are the consequences of manipulating gsb expression in individual NBs? Analysis of gsb mutants and animals with general inappropriate expression of gsb suggest that the gsb locus functions as a molecular switch. However, in these studies the gsb gene was either removed from all cells or expressed in all cells. To better distinguish the contributions of lineage an position in the specification of cell fate, FLP mediated recombination will be used to either eliminate or inappropriately express gsb in individual NB lineages. How do the gsb proteins work with other gene products to specify individual neurons? The even-skipped (eve) gene is specifically activated in the CQ neurons and is dependent on gsb function for its activation. Activation by gsb could be direct or indirect, but since the CA neurons are a small subset of the gsb expressing neurons, additional factors must contribute to the specificity of eve expression in these neurons. The promoter and enhancer elements necessary for eve expression in the CQ neurons will be identified and their regulation studied. How does gsb come to be stably expressed in ten specific NBs per hemisegment? To address this question, the role of gsb protein phosphorylation and its regulation by the products of the patched, zw-3, naked, wingless and hedgehog genes will be analyzed. These studies will provide insight into the process of CNS development and should help to provide a basis for understanding developmental neural disorders.